Prior to the present invention, nonionic water-soluble cellulose ethers have been used in clear underarm stick products. Gel antiperspirant/deodorant sticks typically include a liquid vehicle, an antiperspirant salt and/or deodorant agent, a gelling agent, and one or more emollients. Clear gel antiperspirant or deodorant sticks are more desirable than opaque sticks for cosmetic reasons. For clear sticks, the gelling agents of choice are dibenzylidene alditols, e.g., dibenzylidene sorbitol (DBS), also known as dibenzylidene monosorbitol acetal (DBMSA), because they are able to form strong free standing gels that are clear, are relatively stable, and have relatively good shelf life although they tend to degrade in certain environments. The degradation of the DBS is because of the presence of acidic antiperspirant salt in the stick. Commercially available DBS gel antiperspirant sticks generally contain more than 2% DBS in order to have sufficient hardness. However, such sticks do not have optimum clarity or stability.
Widely used commercially available nonionic water soluble cellulose ethers that are used in antiperspirant/deodorant sticks as co-gelling agents are, for example, methyl cellulose (MC), hydroxypropylmethylcellulose (HPMC), hydroxyethylcellulose (HEC), and hydroxypropylcellulose (HPC); HPC is preferred for clear antiperspirant/deodorant sticks. The use of these prior art cellulose ethers in antiperspirant/deodorant stick products sometimes have processing difficulties such as compatibility with other ingredients, solubility with certain other ingredients, clarity (when needed), and stability under alkaline conditions of the products.
International Publication Number WO 96/26709 and U.S. Pat. Nos. 5,705,171 and 5,725,846 disclose use of hydroxyalkylcellulose and specifically hydroxypropylcellulose in a clear anhydrous antiperspirant stick. U.S. Pat. No. 5,534,245 discloses use of a water-soluble cellulose polymer in a water containing roll-on or soft gel-like antiperspirant.
The stick form can be distinguished from a gel or a paste in that in a stick, the formulated product can maintain its shape for extended period of time outside the package except for the shrinkage due to solvent evaporation. U.S. Pat. No. 5,725,846, 5,705,171, 4,720,381, and 4,725,430 disclose use of hydroxypropylcellulose in a transparent anhydrous antiperspirant stick composition. U.S. Pat. No. 4,383,988 discloses use of hydroxypropylcellulose acetate in water containing pourable antiperspirant gel composition. EP Patent Application 0260030 discloses the use of chemically modified cellulose, such as hydroxypropylcellulose, hydroxyethylcellulose, and methylcellulose in water containing clear deodorant sticks. However, none of the prior art discloses the use of hydrophobically modified polysaccharides in a transparent anhydrous antiperspirant stick.